Desulfurization and dearomatization of hydrocarbon mixtures by solvent extraction



y 14, 1957 LE ROI E. HUTCHINGS 2,792,332 DESULFURIZATION AND DEAROMATIZATION OF HYDROCARBON MIXTURES BY SOLVENT EXTRACTION Filed Dec. 4, 1953 mm A .I .r: T 3 Q vm mm lhn um ..i R Q j h T 3 wv 9. 5 mm mm E Iv Iv HTICI I 3 mm 1 q on 3 fi 3 RNA 2 mm B mv A mm R m mm 2% mm I T .l mQQEEm in C 6n 1 mm b P r w m T 9 w 2 wuwMEm may an .1 Iv V 4? km C mm A h E Q S A n P m. I m .l e m L n. k I

R S m w E m m N C R w w Wm I H T A 5% T mumqzu nited DESULFURIZATION AND DEAROMATIZATHON OF HYDROCARBON MIXTURES BY SOLVENT EXTRACTION Application December 4, 1953, Serial No. 396,287

9 Claims. (Cl. 196-1417) The present invention relates to the liquid phase sol vent extraction of hydrocarbon mixtures to remove aro- PatentO matic constituents and sulfur compounds and, more particularly, relates to a novel solvent combination or composition which has been found particularly effective in treating hydrocarbon mixtures of the class of kerosenes and diesel fuel fractions.

Many processes have been developed for the solvent extraction of crude petroleum, its products, and distillates. in such processes the petrolum hydrocarbons are separated into raffinate fractions of predominately paratfinic nature and extract fractions having a higher concentration of aromatic type hydrocarbons. Lubricating oil stocks are thus freed of aromatic and asphaltic contaminants. Motor fuel distillates of'the gasoline type are improved with respect to their anti-knock qualities by the application of solvent extraction. Cracked naphthas notably rich inaromatics are so treated to obtain the valuable aromatics therefrom. Most of these prior art processesare either specific as to the typeof material being treated, the extraction conditions, or the type or combination of solvents used.

It is well known that these prior art methods, although broadly teaching the application of .solventextraction, are somewhat restricted in actual application as regards the obtaining of the superior results noted. Thus, the solvent extraction of hydrocarbons with alcohols, according to Mann and Chappell in United States Patent 1,163,025, is carried out at a temperature below 32 R, which temperature is obtained by the presence of liquid sulfur dioxide. The use of polyhydric alcohols by Clark and Harding in United States Patent 1,776,550 to remove oxidizable or sludge-producing constituents is confined to treating oils which are substantially free from water. Taveau in United States-Patent 1,825,762 teaches that isopropyl alcohol is a solvent for the pure oil in asphalt .basej residum leaving the asphaltic and other impurities behind and thereby producing valuable lubricatingoils. Arnold teaches that toluene maybe extracted from naphthas of BR ZOO-250 F. by treatment with a solvent consisting essentially of water containing 5 to weight percent of an olefin glycol-as ethylene glycol, the process being conducted 2112450 to 525 F. (United States Patent 2,400,802, George B. Arnold). Stratford and Gurd in United States Patent 2,302,383 teach that dihydric alcohols having at least. two ether groups, as the di-, tri-, and tetraethylene glycols areselective for aromatics being removed from naphtha, kerosene, and light .gas oil. According to with the invention;

Smith in United States Patent 2,444,582, a combination 2,792,332 Patented May 14, 1957 solvent comprising a primary solvent selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, dipropylene glycol, etc., and a secondary solvent containing at least two hydroxyl groups in the molecule being completely miscible with the primary solvent is selective for aromatics present in liquid hydrocarbons.

The processes. heretofore employed, however, have not been-entirely satisfactory especially in the treatment of heavy petroleum naphthas as kerosenes and diesel fuels. It has been'foutnd that for the efiicient desulfurization and aromatic extraction of these materials a particular solvent combination in a relatively limited ratio is required, namely: a solvent comprising a mixture of polyethylene glycol 600 and isopropyl alcohol in the ratio of about 7 to 3, respectively. Polyethylene glycol is a polymer of ethylene glycol having a molecular weight of about 600. Representative material of the general formula HOCHzCl-lz(OCHzCI-IaMOCHsCHsOH index at 20 C. 1.468; SUS at 210 F. 60; SUS atlOO" 300, and flash point 490 F. The molecular weight is determined on the basis of the hydroxyl number.

Accordingly, it becomes a primary object of this invention to provide a process for the desulfurization and dearomatization of heavy naphthas by treatment with a novel solvent combination comprising isopropyl alcohol and polyethylene'glycol 600 in a ratio of about 3 to 7, respectively.

Other objects of this inventionwill become apparent as the description thereof proceeds.

According to the present invention, kerosene and diesel fuel fractions containing considerable amounts of arcmatic hydrocarbons and aromatic-type sulfur compounds are'treated by liquid phase solvent extraction at ambient temperatures using a mixture of polyethylene glycol 600 andisopropyl alcohol found to be highly selective, not requiring an excessive number of treating steps or large amounts of solvent, and capable of producing a sharp out between the non-aromatic and aromatic compounds while exhibiting good solvent power and clean separation. Any non-aromatic sulfur compounds, as mercaptans or sulfides, may be previously removed from the feed hydrocarbons before treatment in accordance In order to demonstrate the invention, a series of experiments are shown wherein a comparison is made of some of the prior art solvents and solvent combinations withthe new solvent mixtures of this invention.

In the following tables, data obtained by conducting a series of batch extractions of Worland, Wyoming diesel fuel and a kerosene: are presented. The Worland, Wyoming dieselfuel (BR 400 to 650 F.) contained 32.3 volume percent of aromatics and was treated with a solvent ratio of 1.4 to 1 at-room temperature. The actual experiments were conducted by placing a cc. sample of the diesel fuel through a batch extraction with cc. of each solvent listed. The ratfinate produced was water washed and analyzed. The extract phase was diluted with water to recoverthe aromatics.

TABLE I Extraction of Worland diesel fuel with various solvents Solvent Analysis of Ratfinatc Compo' Solvent Percent Solvent sltion, Ratio 1 Aromatics Vol. Yield, Vol. Percent Removed Percent Percent Aromatics 1. Polyethylene glycol 600 isopropyl alcohol 70-30 1. 4-1 84 25v 35. 0 2. Ethylene glycol dipropylene glycol 35-65 1.4-1 96 29. 3 13.0 3. Polyethylene glycol 200" lsopropyl alcohol 70-30 1. 4-1 92 27. 4 22.0

1 Indicates solvent-oil ratio.

Table II shows the batchwise extraction of a kerosene having an aromatic content of 19.3 volume percent.

TABLE II Extraction of kerosene with various solvents Vol. Analysis of Rafllnatc Percent Solvent Percent Solvent Solvent Ratio 1 Aromatics Compo- Yield, Vol. Percent Removed sltion Percent Aromatics 4. Polyethylene glycol 600".. 100 1-1 03 13.5 35.0 5. Dlethvlcne glycol 100 1-1 98 17.7 10. 5 0. Polyethylene glycol 600 MEK 72-28 1. 4-1 84 11. 5 49. 9 7. Polyethvlene glycol 600 MEK 52-47 1-1 88 14. 0 36. 2 8. Polyethylene glycol 600 M EK 65-35 2-1 79 10. 5 57- 0 9. Polyethvlenc glycol "600 acetone 72-28 1. 4-1 85 13.0 42. 7 10. Polyethylene glycol 600" Me-isobutvl ketone.-. 72-28 1.4-1 81. 6 14. 5 38. 7 11. Polyethylene glycol 600" isopropyl alcohol 72-28 1. 4-1 79 10.6 57. 0 12. Polyethylene glycol 600 isopropyl alcohol 50-50 1. 4-1 60 ll. 0 65.

1 Indicates solvent-oil ratio.

From the data shown in the tables, it becomes apparent that based on the amount of aromatics removed the solvent combination of polyethylene glycol 600 and isopropyl alcohol in a volume percent relationship of about 70% to is superior to the other solvents tested.

The process of the invention may be carried out either in batchwise extraction or continuous countercurrent extraction. In order to increase the yields of low aromatic product a second step may be used to recover the nonaromatic material from the extract. This step involves contacting the extract phase with polyethylene glycol "600 alone or a mixture of polyethylene glycol "600 and minor amounts of isopropyl alcohol. By operating in this manner a recycle fraction for the first step is obtained along with a pure aromatic product. For example, by conducting a single batch polyethylene glycol 600 extraction of the extract (containing 59.27% aromatics) from a multiple stage extraction of kerosene with polyethylene glycol 600-isopropyl alcohol mixture, an extract containing 88.7% aromatics amounting to 18.1 volume percent and a raifinate of 52.9% aromatics amounting to 81.9 volume percent are obtained. The following Table III represents the data for this type of operation:

TABLE III Batchwise extraction with 1:1 solvent ratio of extract from multistage column TABLE IV Extraction of kerosene with multistage extraction column Solvent Product Percent Percent Solvent Ratio Yield Aromatics Aromatics in Product Removed DEG 3.1 to 1.- 95. 5 13. 1 23. 3 fogGPglgl' hbw 6 to l 82. 7 ll. 4 51. 0 1 5 isopmpyl }2.4 to 1.- 65.0 o. s 67.7

It is seen from these results that the amount of aromatics removed by the combination solvent of the invention far exceeds that of the comparison solvents; that 1 less solvent is needed; and further that substantial amounts of solvent would be required to remove all the aromatics from the product even in a multistage process. Con-j sequently a solvent possessing the properties of the solvent of the instant invention is necessary.

agraasaa The present invention lends itself to a-particular processing technique which most advantageously utilizes the superior properties of the new combination solvent. This may be demonstrated by reference to the attached drawing wherein:

The first stage extraction tower is represented by 1, which is fitted with means to provide intimate contact as Raschig rings, Berl saddles, etc.,and may be divided into at least three separate zones of contact. The charge stock comprising aromatic virgin naphtha; or desulfurized kerosene enters tower lvia line 2 and contacts the combination solvent entering the'topof the tower via line 58 (to be described). The raffinte layer containing the non-aromatichydrocarbons, isopropyl alcohol and a trace of polyethylene glycol 600 is then charged via line 3 to a distillation column 4 where the alcohol is removed and sent by line 5', condenser 6, and line 7 to the alcohol charge tank 8. Some of the alcohol is returned to tower 4 from the condenser 6' as reflux through line 9. The non-aromatic raftinate passes from column 4 via line 10 to column 11 where it is continuously washed with water entering the top from line 12 to produce a finished product (kerosene or diesel fuel or naphtha) which passes over through line 13, through drier 14, and line 15 to storage. The water used in washing'in tower 11 is recycled from the polyethylene glycol"600 recovery steps to be described.

The extract phase from the primary extraction column 1 is sent by line 16 to column 17 wherein the al cohol is removed. Part of the alcohol coming overhead in line 1%, from column 17, is condensed in condenser 19 and returns to the column as reflux through line 20. The balance of alcohol passes via lines 21 and 7 to alcohol storage tank 8. The alcohol-free extract passes from column 17 via line 22 to aromatics recovery steam distillation tower 23. The steam used for'the distillation is made from the wash water from the raffinate washing tower 11 by steam boiler 24, which is connected between the two towers'by line 25. The aromatics and water go overhead to total condenser 26 via line 27 to settling tower 28 wherein the water and aromatics separate. Water is returned to tower 23 as reflux by line 29 and the aromatics pass by line 30 to a second extraction column 31. The polyethylene glycolwater stream from the steam distillation tower 23 is transferred by line 32 to the solvent recovery tower 33 wherein the water is distilled off, passes through line 34'to condenser 35, and line 12 into column 11 where it washes the rafiinate. Part of the water from the condenser 35 is returned via line 36 to tower 33 as reflux.

In the secondary extraction column 31, the aromatics are concentrated using pure polyethylene glycol. Column 31 should provide about three contacting zones similar to those in column 1. A mixture of isopropyl alcohol and polyethylene glycol could be'used in this step if greater solvency is required. However, it has been found that at this stage the aromatics are of greater purity it pure polyethylene glycol is used in the recovery system. The solvent ratio used in column 31 will be such that the raffinate, that is, the non-aromatic rich material will be of about the same aromatic concentration as the charge. This ratio will be again under 5 to l. The polyethylene glycol passes from tank 37 through pump 38, line 39, to column 31. The raffinate from column 31 is passed via line 40 back to line 2 for reprocessing in the system.

The aromatic extract from column 31 passes via line 41 to steam distillation tower 42 for the recovery of aromatics. Purified aromatic overhead from tower 42 passes by line 43 to condenser 44 and settling tower 45. Water refluxed is returned to tower 42 by line 46. Steam for tower 42 is provided by boiler 24 and line 47.

Polyethylene glycol and water in admixture pass through line 48 to tower 49. Tower 33 may also be used for this purpose but normally two towers would be used for convenience. Line 50 carries the water into-condenser 51 from whence it may travel byline 52 back into the system or be returned as reflux-by line 53. Recovered polyethylene glycol from tower Sipassesthrough line 54 to join thatmecovered by tower 49 and passes via line 55 to storage tank 37.

The mixing and proportionating apparatus forthe system comprises pumps56 and 57 which mix the solvents from tanks 8 and 37, which pass vialine 58 to the first stage of column 1. Hydrocarbons and aromatic sulfur compounds leavethe system by line 59.

As more specific examples of the operation. of .the apparatus, the following is given showing material balances:

An' example of the complete operation for kerosene extraction would be as follows. 1,000 bbls./day of a sour kerosene containing 19% aromatics and .65 weight percent sulfur and a recycle fraction from the aromatics concentration step of297 bbls./day (22% aromatics) are contacted with 4,380 bbls./day of aPEG 600f-isopropyl alcohol. mixture (70-30) in a tower containing treating stages equivalent to three countercurrent batchwise stages. A raffinate product containing. 2% aromatics and .1% sulfur (817 bbls./day) is obtained. This product contains 6.5% isopropyl alcohol and a trace of PEG. The alcoholis removed by distillation (60 bbls.) and the PEG is removed by water washing.

The extract product from this step is distilledto remove the' isopropyl alcohol (1,254 bbls./day), and water diluted and steam distilled to remove the aromatics. The PEG (3066 bbls./day) is recovered by distillation. Water fraction arecycled to eliminate solvent losses. The aromatic. product. (.480- bbls./day-50% aromatics)v is extracted in a second tower which has treating stages equivalent to three countercurrent batchwise stages. A solvent ratio of 2 to 1 using pure PEG is used. A pure aromatics extract product (183 bbls./day) is obtained and the remainder,.297 bbls./ day-22% aromatics, is recycled to the first tower. The solvent (960 bbls./day) is recovered from the extract by water dilution and steam distillation.

' The processof the invention is carried out by liquid phase contact of solvent with the hydrocarbons to be treated at ambient temperatures of from 70 to F. and no particular advantage is gained by operating at higher temperatures or through the application of diminished pressures during the distillations. The foregoing description contains a limited number of embodiments of the present invention. It will be understood, however, that numerous variations are possible without departing from the spirit of the following claims:

What is claimed is:

1. A process for the removal of aromatics and sulfur compounds from hydrocarbon mixtures comprising contacting said hydrocarbons with a solvent comprising. a mixture of polyethylene glycol having a molecular weight of about 600 and isopropyl alcohol in volume percent ratios of about 70 to 30, respectively to produce an extract phase and a raffinate phase, and separating an aromatic rich fraction from the extract phase anda parafiinic-naphthenic rich fraction from the raffinate phase and further contacting the aromatic rich fraction with pure polyethylene glycol to obtain a concentrated aromatic fraction and a paraffinic-naphthenic raflinateand recycling said raflinateto said first mentioned hydrocarbon mixture for reprocessing therewith.

2. The process in accordance with claim 1 in which the hydrocarbon mixture comprises a kerosene fraction.

3. The process in accordance with claim 1 in which the hydrocarbon mixture comprises a diesel fuel.

4. The process for the removal of aromatic hydrocarbons and aromatic sulfur-type compounds from hydrocarbon mixtures comprising contacting said hydrocarbons with a solvent comprising a mixture of polyethylene glycol having a molecular weight of about 600 and isopropyl alcohol in volume percent ratios of about 70 to 30, respectively, in a first contact zone to produce an aromatic extract phase and a paraffinic-naphthenic rafiinate phase, subjecting said rafiinate phase to distillation to remove isopropyl alcohol as overhead and produce a parafiinicnaphthenic ratfinate phase, washing said rafiinate phase with water to produce purified hydrocarbons and a water wash phase, subjecting said extract phase to distillation to remove isopropyl alcohol as overhead, recycling the isopropyl alcohol from the distillations to said first contact zone, subjecting the alcohol-free extract phase to steam distillation in the presence of steam produced from said water wash phase, condensing the vapors from said steam distillation and separating an aromatic phase and a water wash phase therefrom, subjecting said aromatic phase to solvent extraction in a second contact zone by contact with polyethylene glycol having a molecular weight of about 600 to produce a second rafiinate phase and a second extract phase, recycling said second raffinate phase to said first contact zone. subjecting said second aromatic phase to steam distillation in the presence of steam produced from said water wash phase to produce an aromatic phase containing aromatic sulfur compounds and a polyethylene glycol-water phase, distilling said polyethylene glycol-water phase to separate water therefrom for recycle to said water wash step and recovering polyethylene glycol for recycle in said process.

5. The process for the removal of aromatic and sulfur compounds from hydrocarbon mixtures comprising contacting said hydrocarbons with a solvent comprising a mixture of polyethylene glycol having a molecular weight of about 600 and isopropyl alcohol in the volume percent ratios of about 70 to 30, respectively, in the liquid phase at a temperature of about 70 to 100 F. in a first contact zone to produce a first extract phase and a first raffinate phase, subjecting said first raffinate phase to distillation to remove isopropyl alcohol therefrom as a distillate and produce a non-aromatic rafiinate phase, washing said non-aromatic raffinate phase with water to produce purified hydrocarbons and a water wash phase, subjecting the first extract phase to distillation to remove isopropyl alcohol therefrom for recycle to said first zone and produce an isopropyl alcohol-free extract phase, subjecting said isopropyl alcohol-free extract phase to steam distillation in the presence of steam produced from said water wash phase, condensing vapors from said steam distillation to separate an aromatic phase and a first water phase, and recovering a polyethylene glycol-water phase from said steam distillation, subjecting said polyethylene glycol-water phase to distillation to produce a second water phase and a polyethylene glycol phase, recycling said second water phase to said water washing step and said polyethylene glycol to said first zone, subjecting said aromatic phase to solvent extraction in a second zone by contact with weight of about 600 to produce a second raflinate phase and a second extract phase, recycling said second rafiinate phase back to said first contact zone, subjecting said second aromatic phase to steam distillation in the presence of steam produced from said water Wash phase to produce a purified aromatic phase containing any aromatic sulfur compounds present and a polyethylene glycolwater phase, distilling said polyethylene glycol-water phase to separate a third water phase for recycle to said water washing step and recovering polyethylene glycol for recycle in said first zone.

6. In the process of separating aromatic hydrocarbons and aromatic sulfur compounds from hydrocarbons wherein said hydrocarbons are contacted in the liquid phase at ambient temperature with a selective solvent comprising a mixture of about 70 volume percent of polyethylene glycol having a molecular weight of about 600 and about 30 volume percent of isppropyl alcohol, to separate a first raifipolyethylene glycol having a molecular nate phase and a first aromatic extract phase, and said phases are further purified by a series of distillation steps including distillation of the first rafiinate phase to remove isopropyl alcohol therefrom, distillation of the first extract phase to remove isopropyl alcohol therefrom with recycle of said isopropyl alcohol to said first contact step, the steps comprising maintaining a common source of Wash water, washing said distilled first raffinate to produce a first water wash phase and purified rafiinate hydrocarbons, vaporizing said first water wash phase to produce steam, utilizing a portion of said steam to steam distill said distilled first extract phase, separating an alcohol-free aromatic phase and a polyethylene glycol-water phase from said first steam distillation, subjecting said alcohol-free aromatic phase to a second extraction with polyethylene glycol having a molecular weight of about 600 to produce a second rafiinate phase for recycle to said first contact step, and a second extract phase to steam distillation in the presence of a portion of steam from said first water phase, separating an aromatic type hydrocarbon fraction and a polyethylene glycol-water phase therefrom and distilling said polyethylene glycol-Water phase to produce pure polyethylene glycol for recycle in said process and a water phase for recycle to said water wash step.

7. A continuous process for reducing the content of aromatic hydrocarbons and aromatic sulfur compounds from hydrocarbon mixtures selected from the group consisting of kerosene fractions and diesel fuels and mixtures thereof which comprises continuously contacting said oil with a solvent comprising a mixture of about 70 volume percent of polyethylene glycol having a molecular weight of about 600 and about 30 volume percent of isopropyl alcohol at a temperature sufiicient to insure liquid phase contact, continuously forming two immiscible phases comprising a lower extract layer of solvent containing a substantial amount of aromatics and sulfur compounds and an upper raflinate layer containing a substantial amount of remaining hydrocarbons and small amounts of solvent mixture, continuously separating said layers and separating an aromatic rich fraction from said lower extract layer and a parafiinic-naphthenic rich fraction from said upper rafiinate layer and further continuously contacting said aromatic rich fraction with pure polyethylene glycol to obtain a purified aromatic fraction and further recovery of the parafiinic-naphthenic portion thereof.

8. The process for the removal of aromatic hydrocarbons and aromatic sulfur-type compounds from hydrocarbon mixtures comprising contacting said hydrocarbons with a solvent comprising a mixture of polyethylene glycol having a molecular weight of about 600 and isopropyl alcohol, in a first contact zone to produce an aromatic extract phase and a paraflinic-naphthenic rafiinate phase, removing isopropyl alcohol from said paratfinic-naphthenic rafiinate phase, washing said raflinate phase with water to produce purified hydrocarbons and a water wash phase, removing isopropyl alcohol from said extract phase for recycle to said first contact zone, subjecting said alcohol-free extract phase to steam distillation in the presence of steam produced from said water wash phase and separating from the overhead an aromatic phase, subjecting said aromatic phaseto solvent extraction in a second contact zone by contact with polyethylene glycol having a molecular weight of about 600m produce a second raffinate phase and a second extract phase, recycling the second raflinate phase for admixture with said first mentioned hydrocarbon mixture, subjecting said second aromatic phase to steam distillation in the presenceof steam produced from said water wash. phase to produce a concentrated aromatic overhead and a polyethylene glycol-Water phase and recovering polyethylene glycol from said latter phase for recycle.

9. The method in accordance with claim 8 in which the water for the washing of said rafiinate phase comprises the condensed water phase produced from the steam dis- 9 1G tillation of said aromatic phase and the water phase re- 2,396,303 Cummings et a1. Mar. 12, 1946 sulting from the recovery of said polyethylene glycol. 2,444,582 Smith July 6, 1948 2,475,147 Manley July 5, 1949 References Cited in the file of this patent 2,497,588 Davies Feb. 14, 1950 UNITED STATES PATENTS 5 2,650,187 igle Aug. 5, 9

2,101,643 Engelke Dec. 7, 1937 

1. A PROCESS FOR THE REMOVAL OF AROMATICS AND SULFUR COMPOUNDS FROM HYDROCARBON MIXTURES COMPRISING CONTACTING SAID HYDROCARBONS WITH A SOLVENT COMPRISING A MIXTURE OF POLYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT OF ABOUT 600 AND ISOPROPYL ALCOHOL IN VOLUME PERCENT RATIOS OF ABOUT 70 TO 30, RESPECTIVELY TO PRODUCE AN EXTRACT PHASE AND A RAFFINATE PHASE, AND SEPARATING AN AROMATIC RICH FRACTION FROM THE EXTRACT PHASE AND A PARAFFINIC-NAPHTHENIC RICH FRACCTION FROM THE RAFFINATE 